Remove Map::cleanup and Painter::cleanup

Both were noops.

src/mbgl/map/map.cpp

@@ -153,7 +153,6 @@ void Map::start() {
         fileSource.clearLoop();
 
         // Closes all open handles on the loop. This means that the loop will automatically terminate.
-        asyncCleanup.reset();
         asyncRender.reset();
         asyncTerminate.reset();
     });
@@ -177,11 +176,6 @@ void Map::start() {
         }
     });
 
-    asyncCleanup = util::make_unique<uv::async>(**loop, [this]() {
-        assert(painter);
-        painter->cleanup();
-    });
-
     thread = std::thread([this]() {
 #ifndef NDEBUG
         mapThread = std::this_thread::get_id();
@@ -276,12 +270,6 @@ void Map::swapped() {
     rerender();
 }
 
-void Map::cleanup() {
-    if (asyncCleanup != nullptr) {
-        asyncCleanup->send();
-    }
-}
-
 void Map::terminate() {
     assert(painter);
     painter->terminate();